Isolates of the fungal pathogen Metarhizium anisopliae (Metschnikoff) Sorokin
were applied into ratoon crops of sugarcane infested with third instar larvae of negatoria
canegrub (Lepidiota negatoria Blackburn), or Childers canegrub (Antitragus
parvulus Britton). Metarhizium conidia and the rice grains on which they were
grown were applied using paired coulters in cane rows. Two strains of the fungus
were tested against each canegrub species, with strain FI147 common to both.
Against negatoria canegrub, a high application rate of FI147 (originally isolated
from L. consobrina Girault) gave grub control and produced cane yields comparable
to chemical insecticides. The alternative strain FI153 (isolated from L. frenchi
Blackburn) did not persist in soil and was ineffective. Against Childers canegrub,
FI114 (isolated from Childers cane grub) was superior to FI147. Metarhizium acted
slowly, and grubs continued to die several months after application. Results are
promising for development of M etarhizium as a biological insecticide, but the
fungus will probably be more successful as a prophylactic rather than a remedial
control.